Northwest Arkansas Democrat-Gazette
The murderous mantis
The fascinating little insect hanging around the hummingbird feeder isn’t there for the sugar water after all
Warning: This report includes descriptions of cannibalism and predation that could upset sensitive readers. Reminder: You have been warned.
Tom Vaughan, a photographer then living in Colorado’s Mancos Valley, kept a hummingbird feeder outside his house.
One morning, he stepped through the portico door and noticed a blackchinned hummingbird dangling from the side of the red plastic feeder.
At first, Vaughan thought he knew what was going on. “I’d previously seen a hummingbird in a state of torpor,” he said, “when it was hanging straight down by its feet, regenerating its batteries, before dropping down and flying off.”
On closer inspection, Vaughan saw that the hummingbird was hanging not by its feet but by its head. And forget about its batteries: The bird was in the grip of a 3-inch-long praying mantis.
The mantis was clinging with its back legs to the rim of the feeder, holding its feathered catch in its powerful, seemingly reverent front legs, and methodically chewing through the hummingbird’s skull.
“It was staring at me as it fed,” Vaughan said. “Of course, I took a picture of it.”
Startled by the clicking shutter, the mantis dropped its meal, crawled under the feeder — and began menacing two hummingbirds on the other side.
“Talk about cognitive dissonance,” Vaughan said. “I always thought of mantises as wonderful things to have in your garden to get rid of bugs, but it turns out they sometimes go for larger prey, too.”
“It gave me new respect for mantises,” he added.
Vaughan’s sentiment is echoed by a cadre of researchers who place mantises in a class of their own among the swarming Class Insecta, and who are discovering a range of skills and predilections that make mantises act as aspiring vertebrates.
Praying mantises are the only insects able to swivel their heads and stare at you. Those piercing eyes are equipped with 3-D vision and a fovea — a centralized concentration of light receptors — the better to focus and track.
A mantis can jump as unerringly as a cat, controlling its trajectory through an intricate series of twists and turns distributed across its legs and body, all to ensure a flawless landing on a ridiculously iffy target nearly every time.
The mantis appetite likewise turns out to leap and bound, with scant regard for food-chain decorum.
By the standard alimentary sequence, insects feed on plants or one another, and then birds hunt down insects. But just as there are carnivorous plants such as the Venus flytrap, mantises prey on hummingbirds and other small-tomiddling birds.
PITY THE BIRDS
In research published by the Wilson Journal of Ornithology in June (bit.ly/2z4YSVL), James V. Remsen of the Museum of Natural Science at Louisiana State University and his colleagues documented 147 cases of mantis-on-bird predation in 13 countries representing all continents but Antarctica — not surprising, Remsen said, since there are no mantises on Antarctica.
Hummingbirds were the most common target, but mantises also went after warblers, sunbirds, honeyeaters, flycatchers, vireos and European robins. Large species such as the Chinese mantis, which grows to 4 inches in length, were the most avid avivores, and females were responsible for virtually all the mantid bird killing observed worldwide. In two reported cases, females multitasked, eating birds while breeding with males.
Some mantises in North America now seem to view hummingbird feeders as happy hunting grounds. Kris Okamoto, a retired nurse in San Juan Capistrano, Calif., recently came running when painter cried out that a praying mantis had snatched a hummingbird from her feeder.
Seeing that the bird was already dead, Okamoto and the boy settled down to watch nature take its course. When the postprandial mantis crept back up the feeder, Okamoto gently pushed it off with a stick. Not good enough.
“It started crawling back toward the feeder,” she said. “So we took it away completely and put it over the fence.”
Researchers emphasize that bird predation by mantises remains rare and is insignificant compared to the carnage linked to, say, free-roaming cats. Nevertheless, that the insects have learned to seek out bird feeders for a meal signifies “another step in cognition,” Remsen said.
“We’re lucky praying mantises aren’t our size.”
A ‘CERTAIN PERSONALITY’
Hunting is a professional trademark of the mantid order: the 2,500 known species are all predators, usually of insects and other small invertebrates. Some mantises chase down their prey, but many are consummate ambush artists, waiting with Zen stillness in the grass or among flowers for the right moment to strike.
Their closest relatives are cockroaches, from which they diverged about 250 million years ago, said Gavin J. Svenson, curator of invertebrate zoology at the Cleveland Museum of Natural History and a leading authority on praying mantises.
The family resemblance can still be seen in the long, slender antennae and the triangular, movie-alien shape of the head, among other features.
But praying mantises rise above the flattened, scuttling posture that makes cockroaches look so … verminy. Praying mantises “are unusually charismatic,” said William D. Brown, who studies them at the State University of New York at Fredonia.
Those large eyes, the way they turn to look at a human, give them a “certain personality” that most insects lack, he added.
Molecular and evolutionary studies suggest that mantises diversified in parallel with angiosperms — not because they had anything to do with flowering plants directly, but in part to more effectively prey on the insects that ate or pollinated the plants. Some mantises evolved to look like showy blossoms, a cancan of deadly come-ons.
Those showoffs don’t like playing wallflower. The orchid mantises of Asia, for example, generally avoid lingering around the flowers they imitate, and instead seek out patches of green vegetation. “They themselves become the flower,” Svenson said. “They’re a conspicuous beacon for pollinating insects.”
The bigger the floral pollinators, the bulkier grew their predatory mantises, the better to catch, control and consume even well-armed bumblebees and wasps.
Other mantises resemble gnarled twigs, scraps of tree bark or decomposing leaves, blending in beautifully with forest underbrush, tree trunk or canopy, a cryptic approach to fool would-be prey and their own predators alike.
The smallest mantises flit around in the leaf litter of Australia and are “no bigger than your pinkie nail,” Svenson said. Yet the stick-mimicking mantises of Africa can be nearly as long as your forearm.
GOOD EYES
Mantises find their prey visually, and their exceptionally sophisticated eyesight has lately caught the attention of researchers. Jenny Read of the Institute of Neuroscience at Newcastle University in Britain and her colleagues recently demonstrated that praying mantises have stereoptic vision — 3-D — the first definitive evidence for the talent shown in an invertebrate.
By seeing in stereo — that is, mentally triangulating the slightly different images received from two eyes into a single line of sight — an animal can get a sense of depth and distance.
“It’s a complex ability, and we’re still trying to understand the algorithms, the calculations, that our own brains use to do it,” Read said.
Yet calculate the mantis clearly does. In experiments that traded charisma for cute, the researchers outfitted praying mantises with tiny homemade 3-D glasses: filters that effectively separated the two images a mantis would see when it looked at a screen.
A mantis will ignore a glowing box on a flat screen when viewing it without the benefit of 3-D glasses, the researchers found. But once the filters were in place, the mantis’ brain was fooled into the illusion of a 3-D object hovering at just the right “catch range,” an inch away, and began striking out into empty space as if at prey.
“Our brain is five orders of magnitude bigger than theirs,” Read said. “So either our visual cortex is doing incredibly impressive things I don’t know about yet, or we could get rid of most of it and replace it with a praying mantis brain.”
Which, if it belonged to a female mantis, would surely cry, Must eat.
FIERCE FEMALES
Behind the female’s bottomless appetite is the extraordinary size of her egg case, or ootheca, a frothy proteinous mass studded with up to 400 eggs that can amount to half her body weight.
The female secretes the bulging capsule onto a twig or other surface, where it hardens and protects the eggs as they develop. The job is so energy-intensive she can rarely manage an encore.
The difficulty of securing enough calories to fabricate an ootheca could help explain why females of some mantid species famously engage in sexual cannibalism — consuming their mates after, or even during, copulation. Whether a male mantis actively sacrifices himself for the sake of his progeny or simply fails to dart away from the female in time remains a topic of active research.
Brown, of SUNY Fredonia, and Katherine L. Barry of Macquarie University in Australia showed that cannibalized males sired about 60 more eggs than did noncannibalized fathers, an increase of 20 percent over the standard ootheca complement of 258 eggs.
The conclusion: If a male, after spending 3 ½ hours in the typical mantis copulatory bout, has a better than 1 in 5 chance of encountering a second fertile female somewhere down the line, reproductive logic dictates that he should channel his inner Olympian and bolt.
Or jump — mantises are good at that, too.